The present invention relates generally to ablation devices that use electromagnetic energy to ablate internal biological tissues. More particularly, the present invention relates to an improved antenna arrangement for controlling the direction of energy delivered to a biological tissue during ablation.
Medical ablation devices have been around for some time. For example, ablation catheters utilizing electromagnetic energy, in both the RF and microwave frequency ranges, have been introduced and employed to various degrees to ablate biological tissues. One common application is to ablate myocardium tissues to treat a variety of cardiac arrhythmias. By way of example, representative microwave ablation catheters are described in the U.S. Pat. Nos. 4,641,649 to Walinsky; U.S. Pat. No. 5,246,438 to Langberg; and U.S. Pat. No. 5,405,346 to Grundy, et al., each of which is incorporated herein by reference.
Most existing microwave ablation catheters contemplate the use of antennas that produce a peripherally extending field that surrounds the catheter. That is, the electromagnetic energy generated by the antenna is propagated laterally to the sides of the catheter relatively uniformly about the antenna region of catheter. Although such catheter designs work well for a number of applications, in many applications it would be desirable to provide a more directional field that concentrates most of the electromagnetic energy generated by the antenna in a predetermined direction.
There have been some efforts to provide catheters and/or other ablation instruments with more directional fields. By way of example, U.S. Pat. No. 5,800,494 to Campbell, et al. and co-pending U.S. application Ser. No. 09/333,747 to Berube (Sep. 23, 1999) describe a number of antenna designs that generate generally forward firing fields. Additionally, U.S. Pat. No. 5,314,466 to Stern, et al, and co-pendingf U.S. application Ser. No. 09/178,066 to Berube, et al. (Jun. 14, 1999) describe antenna designs that generate generally side firing fields. Although such designs work well, there are continuing efforts to improve antenna designs to provide ablation instruments with specific directional components, such as in a lateral direction to one side of the catheter.
During positioning and/or use of the ablation catheter, it is often desirable to monitor certain electrophysiological properties of the heart. To facilitate such electrophysiological monitoring, electrodes are often positioned near the distal end of the catheter. Typically, such electrodes take the form of annular metallic rings. However, in some implementations, the annular rings have been replaced with electrode bands with multiple electrodes per band. By way of example, U.S. Pat. No. 5,788,692 to Campbell, et al. describes a mapping catheter with split electrode bands. Although the existing electrode designs work well, there are continuing efforts to improve their functionality.
To achieve the foregoing and other objects of the invention, an improved antenna arrangement for use in ablation devices is described. The described antenna arrangement is capable of creating an electromagnetic field, which extends to one side of the ablation device. The antenna arrangement includes an antenna and a reflector, which is positioned on a first side of the antenna. The antenna and the reflector are coupled to a suitable transmission line. The antenna and reflector cooperate to direct the majority of the resultant electromagnetic field in a predetermined direction to a second side of the antenna that is opposite the reflector.
The described antenna structure can be used in a wide variety of ablation devices including catheters and various other surgical instruments, which are generally used in procedures relating to the ablation of internal biological tissues. For example, they can be used to ablate tissues in the heart (e.g., cardiac), the brain(e.g., cerebral), the prostate, the stomach, the intestines, the liver and the like.
In some preferred embodiments, the reflector has a substantially arcuate shape that flares towards the antenna. By way of example, reflectors having arc angles in the range of approximately 90 to about 180 degrees work well. Additionally, the reflector is offset from, and extends in parallel to, the antenna. In embodiments that utilize a co-axial cable as the transmission line, the reflector is preferably coupled to the shield portion of the coaxial transmission line.
In some embodiments, the reflector and the antenna extend substantially in parallel longitudinally from the transmission line. In a related embodiment, the distal end of the reflector extends longitudinally to about the distal end of the antenna
In some embodiments, the longitudinal axis of the antenna is offset from the longitudinal axis of the transmission line in a direction away from the reflector. In other embodiments, an impedance matching device is provided to increase the radiation efficiency of the antenna.